A frequency source is a basic signal source of an electronic system, which mainly comprises a fixed point frequency source and a synthetic frequency source. A frequency source can be applied to electronic systems of military, metrology, industrial, consumer, communications networks, automotive, power grid, radar, communications, measurement and control, and navigation, and the like.
With the development of electronic technologies, the requirement of the electronic system for the stability of the frequency generated by the frequency source becomes higher and higher. The frequency stability of the frequency source will directly affect performance of the electronic system. For example, the Cellular Telephone System requires a microsecond-level precision to implement seamless handover synchronously. The Network Time Protocol (NTP) requires a millisecond-level time precision to achieve accurate time control at the application layer. Applications over Internet Protocol (IP), such as audio and video, require fixed frequencies providing good timing information. The frequency deviation for a typical frequency source, such as a crystal oscillator, is within a range of tens or even hundreds of ppm (parts per million). The frequency deviation of the frequency source may cause the performance of the electronic system to degrade.